The present invention relates to the selective hydrogenation of nitriles such as adiponitrile to omega-aminonitriles such as epsilon-aminocapronitrile, employing a Group VIII metal-containing catalyst.
Group VIII noble metals are well known catalysts for various hydrogenations of organic compounds. One such hydrogenation is the complete hydrogenation of adiponitrile to hexamethylenediamine by a platinum or palladium catalyst. While the diamine product is widely used for producing diacid-diamine-type polyamides such as Nylon 66, it would be desirable to also produce from the dinitrile the partial hydrogenation product, epsilon-aminocapronitrile, since this compound could be cyclized into caprolactam and polymerized to produce Nylon-6. While some attempts have been made with certain Group VIII metals or complexes to achieve selective hydrogenation, a process with high selectivity to epsilon-aminocapronitrile, or other omega-aminonitriles, at moderate conversion and with a catalyst which can be easily handled and conveniently recycled have not yet been found.
Rhodium complexes have found few practical applications in hydrogenations. We recently proposed certain rhodium complexes for hydrogenation of anthraquinones as part of a cyclic process to produce hydrogen peroxide in our copending application, U.S. Ser. No. 244,844, filed Mar. 18, 1981 now U.S. Pat. No. 4,336,241. Other rhodium or rhodium-containing catalyzed hydrogenations are disclosed in Paul N. Rylander, Catalytic Hydrogenation In Organic Syntheses (N.Y. 1979) and Brian R. James, Homogeneous Hydrogenation (N.Y. 1973). Rhodium-based catalysts have not, however, been known to selectively hydrogenate dinitriles to aminonitriles.